Thickness Control of Piezoelectric Film Made by Stencil Printing

In various industries such as power plants, ultrasonic non-destructive testing (NDT) is widely used because of cost effectiveness and sub-surface defect/flaw detection capability. Piezoelectric films made of sol-gel composites could be useful as ultrasonic transducers due to high tempearature durability, reasonable signal strength, curved surface suitability, relatively low center frequency such as 2-50MHz, and high signal-to-noise ratio (SNR). However, traditional spray technique required multiple spray coating and thermal treatments until desired film thickness was obtained in order to achieve desired frequency without crack. If thickness limitation by one coating process augmented, fabrication time could be reduced so that it would be more appropriate for industrial applications. Stencil printing is fast and simple method and it could be possible to fabricate thick films by only one coating process. When a sol-gel solution was used for stencil printing, it became more condensed than that for spray technique because suitable viscosity for stencil printing was higher. In the previous studies, Pb(Zr,Ti)O3 (PZT)/PZT, Bi4Ti3O12 (BiT)/PZT, and PbTiO3 (PT)/PZT films were succesfully fabricated by stencil pring. By only one stencil printing process, film thickness and center frequency were obtained ~70-80μm and ~10-23MHz, respectively, however, it was necessary to develop more low-frequency ultrasonic transducers in order to inspect under severe high temperature situations. Therefore, thickness control of sol-gel composite film fabrication by stencil printing was desired. In this study, thickness increase of PZT/PZT film fabricated by stencil printing was attempted. After the fabrication, the sample was heated by a hot plate and ultrasonic performance, such as reflected echoes, and sensitivity at various temperatures were compared and discussed.